In regards to this mandrak eating of story thing, It simply should not be applicable in a vs forum match precisely because its in a neutral universe. This is because it has more to do with DCs metafictional approach to the construction of its stories than the retainment of a particular ability. It isnt viable because it directly clashes with the constraints of the more prevalent method of fictional writing which both Marvel,DC and most other companies regularly adopt and under which most KMC matches take place. For example, in Marvel the stories of its characters cant be eaten because the entire concept of "the story" itself being recognizable and distinct from the characters within it is non existent. Hence for Mandrakk to "eat their stories" we would have to assume that the Marvel characters "story" was a distinct entity that could be affected in the same way a character from DC's can. Consequently we would be disregarding the very nature in which the Marvel character was written and judging based solely on DC writing concepts.
Now vice versa, by invalidating the strategy of "eating the story" we are going against the metafictional construction of Mandrakk by DC. However im sure most will agree that the KMC vs environment is purely fictional and non self reflective environment. Further since the metafictional writing style isnt commonplace across most platforms and companies, when it comes down to choosing the default nature of KMC vs matches, the more regular fictional writing style should be used.